
package org.apache.solr.spelling;

import java.io.IOException;
import java.io.InputStreamReader;
import java.util.List;
import org.apache.lucene.document.Document;
import org.apache.lucene.document.Field;
import org.apache.lucene.document.TextField;
import org.apache.lucene.index.*;
import org.apache.lucene.search.spell.HighFrequencyDictionary;
import org.apache.lucene.search.spell.PlainTextDictionary;
import org.apache.lucene.store.RAMDirectory;
import org.apache.solr.common.util.NamedList;
import org.apache.solr.core.SolrCore;
import org.apache.solr.schema.FieldType;
import org.apache.solr.search.SolrIndexSearcher;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
 * <p>
 * A spell checker implementation that loads words from a text file (one word per line).
 * </p>
 *
 * @since solr 1.3
 **/
public class FileBasedSpellChecker extends AbstractLuceneSpellChecker {

    private static final Logger log = LoggerFactory.getLogger(FileBasedSpellChecker.class);

    public static final String SOURCE_FILE_CHAR_ENCODING = "characterEncoding";
    private String characterEncoding;
    public static final String WORD_FIELD_NAME = "word";

    @Override
    public String init(NamedList config, SolrCore core) {

        super.init(config, core);
        characterEncoding = (String) config.get(SOURCE_FILE_CHAR_ENCODING);
        return name;
    }

    @Override
    public void build(SolrCore core, SolrIndexSearcher searcher) throws IOException {

        loadExternalFileDictionary(core);
        spellChecker.clearIndex();
        // TODO: you should be able to specify the IWC params?
        // TODO: if we enable this, codec gets angry since field won't exist in the schema
        // config.setCodec(core.getCodec());
        spellChecker.indexDictionary(dictionary, new IndexWriterConfig(core.getSolrConfig().luceneMatchVersion, null), false);
    }

    /**
     * Override to return null, since there is no reader associated with a file
     * based index
     */
    @Override
    protected IndexReader determineReader(IndexReader reader) {
        return null;
    }

    private void loadExternalFileDictionary(SolrCore core) {

        try {
            // Get the field's analyzer
            if (fieldTypeName != null && core.getSchema().getFieldTypeNoEx(fieldTypeName) != null) {
                FieldType fieldType = core.getSchema().getFieldTypes().get(fieldTypeName);
                // Do index-time analysis using the given fieldType's analyzer
                RAMDirectory ramDir = new RAMDirectory();

                LogMergePolicy mp = new LogByteSizeMergePolicy();
                mp.setMergeFactor(300);
                try (IndexWriter writer = new IndexWriter(
                             ramDir,
                             new IndexWriterConfig(core.getSolrConfig().luceneMatchVersion, fieldType.getAnalyzer()).
                             setMaxBufferedDocs(150).
                             setMergePolicy(mp).
                             setOpenMode(IndexWriterConfig.OpenMode.CREATE) // TODO: if we enable this, codec gets angry since field won't exist in the schema
                             // .setCodec(core.getCodec())
                             )) {
                    List<String> lines = core.getResourceLoader().getLines(sourceLocation, characterEncoding);

                    for (String s : lines) {
                        Document d = new Document();
                        d.add(new TextField(WORD_FIELD_NAME, s, Field.Store.NO));
                        writer.addDocument(d);
                    }
                    writer.forceMerge(1);
                }

                dictionary = new HighFrequencyDictionary(DirectoryReader.open(ramDir),
                        WORD_FIELD_NAME, 0.0f);
            }
            else {
                // check if character encoding is defined
                if (characterEncoding == null) {
                    dictionary = new PlainTextDictionary(core.getResourceLoader().openResource(sourceLocation));
                }
                else {
                    dictionary = new PlainTextDictionary(new InputStreamReader(core.getResourceLoader().openResource(sourceLocation), characterEncoding));
                }
            }
        }
        catch (IOException e) {
            log.error("Unable to load spellings", e);
        }
    }

    public String getCharacterEncoding() {
        return characterEncoding;
    }
}
